Gas turbine engine ducting arrangement having discrete insert

ABSTRACT

A ducting arrangement ( 10 ), including: a plurality of discrete ducts ( 18 ), each defining a flow path and configured to receive a flow of combustion gases from a respective combustor can, where the plurality of discrete ducts merge to form a common duct structure; and a throat insert ( 50 ) configured to define at least part of a junction of one of the discrete ducts and the common duct structure.

STATEMENT REGARDING FEDERALLY SPONSORED DEVELOPMENT

Development for this invention was supported in part by Contract No.DE-FC26-05NT42644, awarded by the United States Department of Energy.Accordingly, the United States Government may have certain rights inthis invention.

FIELD OF THE INVENTION

The present invention relates to a combustion gas duct that includes adiscrete insert having a different mechanical property than a remainderof the duct. The combustion gas duct may be formed by bi-casting ductmaterial around the insert.

BACKGROUND OF THE INVENTION

Conventional can-annular gas turbine engines include a plurality ofindividual combustor cans, where each can is secured to a respectivetransition duct that directs combustion gases from the combustor can,and through inlet guide vanes to a respective portion of a turbine inletannulus. Each flow of combustion gas remains discrete from the combustoruntil exiting the respective transition duct. In contrast, in certainemerging gas turbine engines that use can combustors, the cans arerepositioned such that combustion gas flows exiting the cans is alreadyproperly oriented for delivery onto the first row of turbine blades. Anexample of this may be seen in US Patent Application Publication Number2011/0203282 to Charron et al., published Aug. 25, 2011, which isincorporated by reference in its entirety herein. The array oftransition ducts are replaced with a duct arrangement that receives thediscrete combustion gas flows, accelerates them to a speed appropriatefor delivery onto the first row of turbine blades, and directs them intoa common annular chamber where the combustion gas flows are no longersegregated from each other. The annular chamber exhausts directly intothe turbine inlet. The proper orientation and speed created by thearrangement eliminates the need for a first row of inlet guide vanespresent in the conventional arrangements

In conventional gas turbine engine combustor arrangements, since thecompressed air flows are not accelerated in the transition ducts thereis a relatively small static pressure difference between compressed airin the plenum surrounding the transition duct and a static pressure ofthe combustion gas flows within the transition. Consequently, there is arelatively small force pressing inward on the exterior surface of thetransition ducts.

In contrast, in the emerging technology ducting arrangement thecombustion gas flows are traveling at significantly greater speeds. Thisresults in significantly greater pressure differences (up to sixatmospheres) and resulting forces acting on the exterior surface of theducting arrangement. The annular chamber experiences the greatest ofthese forces because the combustion gas flows are fully acceleratedwithin the annular chamber. These forces act to deform the ductingarrangement and hence there is room in the art for improvements thatresist this deformation.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is explained in the following description in view of thedrawings that show:

FIG. 1 is a schematic representation of an exemplary embodiment of theducting arrangement that may use the insert described herein.

FIG. 2 is a schematic representation of the combustion arrangement ofFIG. 1 positioned within a combustion section of a gas turbine engine.

FIG. 3 shows a single ducting arrangement subcomponent of the ductingarrangement of FIG. 1.

FIG. 4 is an exemplary embodiment of the downstream end of the ductingarrangement subcomponent of FIG. 3 showing an exemplary embodiment ofthe insert.

FIGS. 5-7 show various angles of the insert of FIG. 4.

FIG. 8 shows a close-up in the junction indicated in FIG. 3 and shows anexemplary embodiment of a cooling channel formed in the junction.

DETAILED DESCRIPTION OF THE INVENTION

The present inventors have recognized at least one form of deformationthat may occur when using one exemplary embodiment of a ductingarrangement and have identified a region of the ducting arrangementlikely to experience substantial mechanical stresses as a result of thisdeformation. The inventors have further recognized that this region ofrelatively great mechanical stress is also a region of relatively greatthermal stress which compounds the problem.

To accommodate this localized region of high mechanical and thermalstresses, and thereby extend the service life of the ductingarrangement, the inventors have proposed an innovative arrangement thatlowers the mechanical stresses in the area. This, in turn, permits theuse of an insert having a material that is better suited thermally forthe local region, and this reduces an amount of cooling air that isrequired for the local region which, in turn, increases engineefficiency. Reducing the stresses at this location permits the use of aninsert material that may possess a different mechanical property, forexample a lower yield strength, when compared to a material of theducting arrangement immediately surrounding the insert. The inventorshave also proposed to thermally decouple the insert from the material ofthe ducting arrangement immediately surrounding the insert. This willreduce thermal growth mismatch and associated stresses, furtherextending the service life of the component.

These goals may be accomplished in one exemplary embodiment bybi-casting ducting material around the insert. Bi-casting securely locksthe insert in place but does so without a metallurgical bond. This canpartially or fully structurally and/or thermally decouple the insertfrom the remainder of the ducting arrangement. This, in turn, permitsthe selection of a material for the insert that is tailored to withstandthe relatively harsh conditions present in the region, (greaterhigh-temperature stability) while allowing the selection of differentmaterial sufficient to withstand the relatively less harsh conditions inthe remainder of the ducting arrangement. This is particularlybeneficial in terms of cost since it allows for the use of the moreexpensive material of the insert only where conditions require it, whileless expensive material can be used elsewhere.

FIG. 1 is a schematic representation of an exemplary embodiment of aducting arrangement 10 that may be used with properly oriented cancombustors (not shown), viewed looking from aft to fore. The ductingarrangement 10 receives combustion gases and guides them toward an inletannulus (not shown) of a turbine (not shown). The ducting arrangement 10may include a plurality of cones 12, each configured to receive adiscrete flow of combustion gases emanating from a respective cancombustor. Each cone 12 may deliver the respective flow of combustiongases to an annular chamber 14 into which all combustion gas flows flow.An accelerating configuration 16 may be present to accelerate acombustion flow from a speed at which it travels when entering the cone12 to a speed appropriate for delivery onto a first row of turbineblades (not shown), which could approach 0.8 mach and above. In thisexemplary embodiment each cone 12 forms part of a respective discreteduct 18, where each discrete duct 18 ends where the annular chamber 14is first encountered. The portion of the ducting arrangement from thispoint downstream is the common duct structure which, in this exemplaryembodiment, includes the annular chamber 14.

FIG. 2 shows the ducting arrangement 10 (without the cones 12 forclarify) positioned within a turbine vane carrier 20 of a gas turbineengine. Compressed air exits a compressor exit diffuser 22 and enters aplenum 24 surrounding the ducting arrangement 10. The compressed air ismoving relatively slowly in the plenum 24 as it moves toward an inlet(not shown) to the combustor cans (not shown). Once the compressed airis mixed with fuel and combusted in the can it is received by theducting arrangement 10 and accelerated to a relatively fast speedapproaching mach 0.8 and above via the accelerating configuration 16partly visible in FIG. 2. Partially visible within the turbine vanecarrier 20 is the annular chamber 14 which experiences the bulk of thepressure induced forces. The cone ends of the ducting arrangement 10 areessentially fixed axially by the can combustors and associatedstructure. Consequently, the pressure of the compressed air in theplenum 24 not only presses on all exterior surfaces of the ductingarrangement 10, it also tends to push the annular chamber 14 aft intothe turbine inlet annulus. The result is a cantilever-like “prying” ofthe discrete flow ducts portion of the ducting arrangement 10 from theannular chamber 14.

FIG. 3 shows one exemplary embodiment of the ducting arrangementsubcomponent 30 that includes one cone 12 at a cone end 32 and onecommon duct structure end 34. Within the common duct structure end 34 isan arc-segment 36 that forms part of the annular chamber 14 when aplurality of the ducting arrangement subcomponents 30 are assembledtogether and a discrete flow path portion 38 leading to the arc-segment36. (Other exemplary embodiments exist where a common duct structure isformed but it does not take the form of the annular chamber 14.) Wherewalls 40 of the discrete flow path portion 38 intersect with walls 42 ofthe arc-segment 36 a junction 44 is formed. Upon reaching a junction 44combustion gases from adjacent flows are not prevented from mixing byduct structure. If each flow were theoretically fully collimated,incompressible, and without momentum, then adjacent flows would likelynot mix. However, it is expected that some mixing may occur due toexpansion, shear interactions, and a momentum-induced flattening of theflow as it is turned by the annular chamber 14 against its wish tocontinue flowing along a straight path. At an upstream region 46 of thejunction 44 it can be seen that corners 48 of merging walls 40, 42intersect at a relatively small angle and this angle results in theupstream region 46 taking on the shape of a fillet, which is a stressriser. This fillet is located in a region of the ducting arrangement 10subject to the “prying” action of the discrete flow path portion 38 fromthe common duct structure end 34 as a result of the pressure differencepushing the annular chamber 14 aft (out of the page in this view).

FIG. 4 shows a perspective view of the common duct structure end 34(only) of the ducting arrangement subcomponent 30 from a differentangle. In this exemplary embodiment an insert 50 has been positioned inthe common duct structure end 34 and shaped so that it includes theupstream region 46 of the junction 44. The common duct structure end 34includes the insert 50 and a remainder 52 of the common duct structureend 34. The remainder 52 of the common duct structure end 34 is simplythat part of the common duct structure end 34 not including the insert,(the common duct structure end 34 with the opening for the insert 50).The annular chamber 14 (common duct structure) includes the inserts 50and a remainder (not shown) of the annular chamber 14. The remainder ofthe annular chamber 14 is simply that part of the annular chamber 14 notincluding the inserts 50, (the annular chamber 14 with the openings forthe insert 50). Likewise, the ducting arrangement 10 includes theinserts 50 and a remainder (not shown) of the ducting arrangement 10.The remainder of the ducting arrangement 10 is simply that part of theducting arrangement 10 not including the inserts 50, (the ductingarrangement 10 with the openings for the insert 50).

The opening for a respective insert 50 essentially matches a shape ofthe respective insert 50 that rests therein. The insert 50 and theremainder 52 of the common duct structure end 34 meet at an interface54. The insert may include the upstream region 46 of the junction 44,and the upstream region 46 experiences relatively high temperatures whencompared to other locations of the ducting arrangement 10. Consequently,even if a same material is used for the insert 50 and the material thatdefines the opening, the upstream region 46 may expand or contractdifferently than other locations of the ducting arrangement. In order toprevent excessive thermal growth mismatch, where relative growth causesinternal stresses beyond a yield strength of either material, theducting arrangement 10 may include a gap (not visible) between theinsert 50 and a perimeter 56 of the opening at one temperature. The gapmay shrink and/or disappear at another operating condition. This can beconfigured such that when the gap disappears there is no stress createdin the insert 50, or only an amount of stress that is within the yieldstrength of the insert material. The gap may be uniform around theinsert 50, or it may be locally tailored to accommodate thermal growththat may not be uniform. For example, if the geometry of the insertresults in greater thermal growth in one direction over another, the gapmay be sized to accommodate the local differences. Conversely, thearrangement can be configured such that a yield strength of the ductingmaterial surrounding the insert 50 is not exceeded.

Accommodating the relative thermal growth may be particularly importantwhen the insert material is relatively weaker than the ducting materialthat defines the opening. In this case it is important to ensure a yieldstrength of the insert 50 is not exceeded as a result of the insert 50thermally growing into the perimeter 56 of the opening and thenexperiencing a compressive force imparted by the ducting material thatmay resist that thermal growth. While it is possible that the ductingmaterial that defines the opening may have a lower yield strength, it ismore likely that the material of the throat insert will have a loweryield strength that must not be exceeded. A lower yield strength oftenaccompanies materials characterized by a better high-temperaturestability. High temperature stability materials do not oxidize ordisintegrate as quickly at higher temperatures. General examples of hightemperature stability materials include oxide dispersion strengthenedalloys and ceramic matrix composites. CMSX-4® (of the Cannon MuskegonCorporation, Muskegon Mich.), is an example high temperature stablematerial that may be used for the insert 50. An example of a materialfor the remainder 52 of the common duct structure end 34 is Inconel® 939(of the Special Metals Corporation of Huntington W. Va.).

If the insert 50 and the ducting material that defines the perimeter 56have different coefficients of thermal expansion, this relationship canalso be exploited in order to control stresses in the insert. Forexample, the insert material may have a relatively small coefficient ofthermal expansion when compared to the ducting material defining theopening. The ducting arrangement 10 can be configured such that thegreater temperature increase experienced by the insert 50 and the lowercoefficient of thermal expansion result in a thermal growth that equals(or is essentially equal to) a thermal growth of the ducting materialthat defines the opening, because it has a lesser temperature increasebut a greater coefficient of thermal expansion. Controlling thesefactors can enable control of the amount of stress within the insert 50so that a yield strength of the material of the insert 50 is notexceeded.

In an exemplary embodiment the common duct structure end 34 may beformed by bi-casting ducting material around the throat insert 50, wherethe throat insert 50 was previously cast. Such a bi-casting process isdisclosed in U.S. Patent Application Publication Number 2011/0243724 toCampbell et al., published Oct. 6, 2011, which is incorporated byreference in its entirety herein. The bi-casting process necessarilyoccurs at elevated temperatures. However, a temperature of the insert 50can be controlled in order to maintain a desired relationship betweenthe thermal growth of the insert 50 and the remainder 52 of the commonduct structure end 34. For example, in an instance when the insertmaterial is characterized by a higher coefficient of thermal expansion,a temperature of the insert 50 may be elevated during the bi-castingsuch that the insert 50 has grown thermally to approximate a conditionthe insert 50 will experience during operation of the gas turbineengine. Both the insert 50 and the ducting material would cool toambient temperatures, and the insert would contract more. A gap may beformed at lower temperatures, and this gap may be configured to fullydisappear at operating conditions without the insert expanding to thepoint where it expands into the perimeter 56 of the opening. Expandinginto the perimeter 56 would produce a compressive stress on the insert50 that may not be desired. Alternately, a certain amount of thermalgrowth interference between the two may be desired, and could becontrolled such that the resulting compressive stress did not exceed ayield strength of either material. This can be accomplished by heatingthe insert 50 to a lower temperature than in the last example. Duringsubsequent operation the insert 50 would heat more and thereby grow moreinto the ducting material surrounding the insert 50. Should the insert50 be characterized by a lower coefficient of thermal expansion, keepingthe insert 50 cooler during the casting operation may permit it toexpand more during subsequent operation, thereby minimizing any gapformed at the interface 54. Using these techniques and known variationscan result in an insert that is thermally decoupled from, or lessthermally coupled with the remainder 52 of the common duct structure end34.

Bi-casting in this manner will trap the insert 50 in place but will doso without forming a metallurgical bond at the interface 54 of theinsert and the ducting material defining the opening. As shown in FIG.5, an interlocking feature such as a groove 58 can be formed in aninterface surface 60 of the insert 50, which will geometricallyinterlock with the ducting material that is bi-cast around the insert50. This can be made to form a tortuous path for any air that leaksthrough the interface 54, thereby slowing the rate of leakage.

In a ducting arrangement 10 without the insert 50 a small angle 62 isformed by the corners 48 of the merging walls 40, 42 and this is astress riser 64 that experiences relatively high mechanical stress whenoperating forces act on the discrete ducts, such as to increase thesmall angle 62. In the exemplary embodiment, the insert 50 includes thestress riser 64 of the upstream region 46 of the junction and a length66 of the junction 44 from where the corners 48 begin to intersect untilthey have fully run together inside the common duct structure end 34.Such an insert 50 may be termed a throat insert. Since the insert 50 nowincludes this upstream region 46 of the junction 44, and since theinsert 50 is not metallurgically bonded to the remainder 52 of thecommon duct structure end 34, the remainder 52 does not experience thestiffness of the upstream portion 46 of the junction 44 to the sameextent as it would without the insert 50, and conversely, the remainder52 does not transfer stresses to the upstream region 46 of the junction44 to the same extent as without the insert 50.

The ducting arrangement 10 must then be configured to accommodate thisinterface 54 that is not characterized by a metallurgical bond and hencetransfers load less effectively. To do so the remainder 52 of the commonduct structure end 34 may be made flexible enough to flex yet withstandoperating forces the ducting arrangement 10 experiences during operationincluding the cantilever prying action. Alternately, or in addition, theducting material in the portion of the remainder 52 of the common ductstructure end 34 that surrounds the insert 50 may be thickened toincrease a structural strength of the remainder 52. In this way theupstream region 46 of the junction 44 is mechanically decoupled, orcoupled to a lesser degree, with the remainder 52 of the common ductstructure end 34 when compared to ducting arrangements 10 not having theinsert 50. Consequently, the upstream region 46 of the junctionexperiences reduced stresses during operation. Lowering the stressexperienced increases the number of materials can be used for the insertbecause many materials that satisfy the high temperature arecharacterized by lower yield strengths. Many of these lower yieldstrengths are satisfactory for use in the mechanically decoupled (orless-coupled) configuration but would not be satisfactory without themechanical decoupling (or decreased coupling). Mechanical loads andthermal growth mismatch both contribute to the stresses in the upstreamregion 46 of the junction. Consequently, optimal designs can balance theamount of mechanical decoupling, thermal decoupling, high temperaturetolerance of the material, and yield strength to reach an appropriateconfiguration. In another exemplary embodiment the ducting arrangement10 may be configured such that the insert 50 experiences stressesassociated only with its aerodynamic function.

In this exemplary embodiment the insert 50 also uniquely defines aportion 70 of a flow path 72 associated with the discrete flow pathportion 38 as well as a portion 74 of a flow path 76 associated with thearc-segment 36, and hence with the annular chamber 14 and the commonduct structure.

FIG. 6 shows a different view of the insert 50 looking at the upstreamregion 46 of the junction 44 and the stress riser 64. A corner 80 of theflow path 72 associated with the discrete flow path portion 38 and acorner 80 the flow path 76 associated with the arc-segment 36 actuallymerge with each other at a converging flow junction 84. The respectiveflow paths 72, 76 do not necessarily intersect each other here, butinstead may be configured to share a common plane, though the flows ofcombustion gases in the respective flow paths 72, 76 may blend viaexpansion, shear, and momentum etc.

Separately forming the insert 50 provides yet another advantage. Theupstream region 46 of the junction 44 experiences relatively highoperating temperatures. While the remainder 52 of the common ductstructure end 34 and the remainder of the ducting arrangement 10 may ormay not require cooling, the upstream region 46 may benefit fromcooling. However, when the upstream region 46 is cast with the remainder52 of the of the common duct structure end 34 any cooling channels mustbe machined in subsequent to the casting operation. In contrast, whenthe insert 50 is cast separately, cooling channels can be cast using afugitive casting insert. As a result, the cooling channels can be morecomplex and can incorporate features in a surface of the cooling channelsuch as pins, fins, and turbulators to increase a cooling effectiveness.

FIG. 8 shows a schematic representation of a cooling arrangement 100 inthe insert 50 having a cooling air channel 102. Cooling features 104 inthe cooling channel 104 may increase a surface area of a cooling channelsurface 106 to increase cooling efficiency, and may further increase thecooling efficiency by causing turbulence in the cooling air. Forming thecooling channel 102 and cooling features 104 during a casting operationallows for more detail and ease of manufacturing than is possiblethrough machining methods, such as STEM drilling, and avoids secondaryoperations such as weld plugging etc. While a single cooling air channel102 is shown, the number and arrangement of cooling channels used canvary as needed.

From the foregoing it can be seen that the inventors have recognized anew problem associated with an emerging technology, have created asolution, and have done so using existing technology but applying it ina novel manner. The solution increases service life and improves coolingefficiency and so it represents an improvement in the art.

While various embodiments of the present invention have been shown anddescribed herein, it will be obvious that such embodiments are providedby way of example only. Numerous variations, changes and substitutionsmay be made without departing from the invention herein. Accordingly, itis intended that the invention be limited only by the spirit and scopeof the appended claims.

The invention claimed is:
 1. A ducting arrangement, comprising: aplurality of discrete ducts, each defining a flow path and configured toreceive a flow of combustion gases from a respective combustor can,wherein the plurality of discrete ducts merge to form a common ductstructure; and a throat insert configured to define at least part of ajunction of one of the discrete ducts and the common duct structure. 2.The ducting arrangement of claim 1, wherein the ducting arrangement isformed by bicasting ducting material around the throat insert.
 3. Theducting arrangement of claim 1, wherein the throat insert is configuredto define part of a flow path associated with the one discrete duct. 4.The ducting arrangement of claim 1, wherein the throat insert comprisesan intersection of a corner of the one discrete duct and a corner of thecommon duct structure.
 5. The ducting arrangement of claim 1, wherein athroat material of the throat insert comprises a different mechanicalproperty than a ducting material immediately surrounding the throatinsert.
 6. The ducting arrangement of claim 1, further comprising anexpansion gap between the throat insert and ducting material surroundingthe throat insert effective to prevent internal stress in the throatinsert from exceeding a yield strength of a material of the throatinsert.
 7. The ducting arrangement of claim 1, wherein an interfacebetween the throat insert and a remainder of the ducting arrangementforms a tortuous path.
 8. The ducting arrangement of claim 1, wherein aninterface between the throat insert and a remainder of the ductingarrangement forms a geometric interlock effective to secure the throatinsert in place.
 9. A ducting arrangement, comprising: a plurality ofdiscrete ducts, each defining a flow path configured to receive a flowof combustion gases from a respective combustor can; a common ductstructure into which the plurality of discrete ducts merge; and aplurality of discrete throat inserts, each configured to define at leastpart of a junction between one of the discrete ducts and the common ductstructure, wherein the ducting arrangement is configured to structurallycompensate for a non-metallurgical bond at an interface of the discretethroat inserts with a remainder of the ducting arrangement.
 10. Theducting arrangement of claim 9, wherein the ducting arrangement isformed by bi-casting ducting material around the plurality of discretethroat inserts.
 11. The ducting arrangement of claim 9, wherein theducting arrangement is configured to flex in order to structurallycompensate for the non-metallurgical bond.
 12. The ducting arrangementof claim 9, wherein a portion of the ducting arrangement immediatelysurrounding the throat inserts is thickened with respect to a remainderof the ducting arrangement to structurally compensate for thenon-metallurgical bond.
 13. The ducting arrangement of claim 9, whereina throat material of the throat inserts comprises a greaterhigh-temperature stability than a ducting material in which the throatinserts reside.
 14. The ducting arrangement of claim 9, wherein ductingmaterial defines a plurality of openings in each of which a respectivethroat insert resides, and wherein each opening is sized to permitthermal growth interference between the throat insert and the ductingmaterial without exceeding a yield strength of a material of the throatinsert.
 15. The ducting arrangement of claim 9, wherein each throatinsert defines a portion of a flow path associated with a respectivediscrete duct.
 16. A ducting arrangement, comprising: a ductingarrangement subcomponent comprising a discrete duct and a downstreamend, the discrete duct defining a flow path and configured to receive aflow of combustion gases from a respective combustor can, wherein thedownstream end constitutes part of a common duct structure configured todeliver combustion gases to a turbine inlet annulus when assembled toother ducting arrangement subcomponents; and a throat insert disposedconfigured to define at least part of a junction of the discrete ductand the downstream end, wherein the junction is formed by bi-casting aducting material around the throat insert.
 17. The ducting arrangementof claim 16, wherein a throat material of the throat insert comprises areduced yield strength relative to the ducting material.
 18. The ductingarrangement of claim 16, wherein a throat material comprises anincreased high-temperature stability relative to a remainder of thejunction.
 19. The ducting arrangement of claim 16, wherein the throatinsert and a remainder of the ducting arrangement are free to thermallygrow relative to each other.
 20. The ducting arrangement of claim 16,wherein the throat insert and the ducting material around the throatinsert are configured to accommodate thermal growth interference therebetween without exceeding a yield strength of the throat insert.